Gas turbines are known as xe2x80x9cair machinesxe2x80x9d. They consume very large quantities of air. Even if extensive air filtering is utilized, particles such as dirt, impurities or smoke entrained in the air can combine with water or oil vapors and deposit on the stationary and rotating airfoils in the compressor section. These deposits are usually concentrated in the first 7 or 8 stages of the compressor. After the 7th or 8th stage, the temperature of the compressed air is too hot for the water or oil vapor to remain xe2x80x9cstickyxe2x80x9d and they just travel on through the engine with little impact on operation or performance. The vapor and particles that stick to the airfoils in the 1st through 8th stage can accumulate and cause a rough surface. Just as it is important for an airplane""s wings to have a smooth surface, the same is true for the airfoils in a gas turbine. Rough surfaces reduce airflow and adversely affect engine performance (i.e. decrease fuel efficiency and power output). For this reason gas turbine compressors are routinely washed.
Gas turbines are usually washed by spraying water and detergent into the inlet of the gas turbine while it is spinning. In some cases the engine is running at full speed, in others, it is running or spinning (sometimes just on its starting motor) at a reduced speed. In both cases, water and detergent is sprayed down the throat of the compressor. The washing action always comes from the same direction or angle.
I developed the idea for the inside out compressor cleaning after observation of fouled gas turbine compressors and information I learned while researching for a technical paper I published pertaining to the effect of rough airfoils in the turbine section of a gas turbine. My research revealed that rough surfaces affected gas turbine performance most when this roughness was located on the low pressure (suction or convex) surfaces of the airfoils (blading), especially nearer to the trailing edge. I examined operational gas turbine compressors and noticed more dirt build up and roughness on the low pressure side of the airfoils, more toward the trailing edges. Further research revealed that roughness in this area is critical to all airfoilsxe2x80x94not just the turbine airfoils presented in my research paper. It is in this diverging part of the airflow where the flow can change from laminar to turbulent very easily (due to a rough surface). See FIG. 2. Turbulent flow is a main contributor to friction drag and subsequent loss of airfoil performance.
I examined gas turbine compressor rotor and to study the flow of water and detergent droplets as they would flow through the compressor during conventional washing operations. I discovered that the heavier mass droplets would impact little on the low pressure (diverging or convex) sides of the airfoils. This is because much like a centrifugal separator, the droplets don""t make flow direction changes as readily as a gas (in this case, air). They do not fill into diverging or expanding areas, thus providing critical impact or xe2x80x9cpushxe2x80x9d needed for cleaning action. I realized at this point that one of the most critical surfaces on the airfoil was being neglected by conventional cleaning methods. I figured if we could clean from the back forward (inside out), we could get the low pressure surfaced cleaner (less rough). Looking down the throat of a compressor you wouldn""t think you could insert a hose past several stages of blading. The blading looks too staggered to penetrate with a hose. Additionally, if a hose got stuck in the compressor, you may have to remove the compressor rotor to get the hose out; a costly operation. But with a specially designed and constructed hose/nozzle assembly you can patiently insert (snake) the hose 7 or 8 stages (14 to 16 rows of blading or airfoils) into the compressor. This is repeated between adjacent sets of blades and vanes around the entire periphery of the compressor inlet.
The inside out gas turbine cleaning method is a new method to clean axial gas turbine compressors. This is done by inserting a specially and fabricated flexible hose with nozzles on it into the first several stages of an off line gas turbine compressor. High pressure hot water with detergent is supplied to the hose and as it is withdrawn from the compressor it blasts dirt from the airfoil surfaces in the compressor. Conventional cleaning sprays water in one direction down the throat of the gas turbine compressor, whereas this method cleans from the back forward giving a different blast angle with higher pressure water (see FIG. 1). Using both the conventional cleaning method and this new process, the compressor can be cleaned better allowing for improved gas turbine power and fuel efficiency.